Fouss has one year left, right?
Young is going to be moving to his own offense, but I suspect he's also going to do what he can to have the most success with the players on the team. It would surprise me if there were a little bit of a transition his first year - using sets and plays that work best with the players he's got while he's working to bring in the players he needs to run it 100% his way.
So it may make more sense to keep a guy like Fouss for one year than it does to bring in a guy like Davis who is just starting and would (hopefully) be there for 4 years.
I'm not saying any of that is true - neither you or I know what's going on. I'm just saying there are plausible explanations as to why he would keep Fouss and not bring in Davis - assuming that is what's going on.